In industries where aggressive acids, high chloride concentrations, and continuous corrosion risk define daily operations, standard stainless steels often fall short. Stainless Steel 904L Flanges are engineered precisely for such demanding service conditions, offering exceptional resistance to corrosion while maintaining excellent fabrication and mechanical performance.
Widely specified in chemical processing, oil & gas, marine, pharmaceutical, and power generation sectors, Stainless Steel 904L flanges are trusted by engineers and procurement professionals worldwide for their reliability, longevity, and compliance with international standards. This comprehensive guide explains the metallurgy, properties, standards, applications, and manufacturing practices behind 904L flanges—helping buyers make technically sound and commercially confident decisions.
What Is Stainless Steel 904L Flanges?
Stainless Steel 904L Flanges are pipe flanges manufactured from 904L, a high-alloy, low-carbon austenitic stainless steel developed specifically to resist strong reducing acids and chloride-rich environments.
Alloy & Grade Details
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Material Grade: Stainless Steel 904L
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UNS Designation: UNS N08904
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EN / DIN Equivalent: EN 1.4539
904L contains high levels of nickel, chromium, and molybdenum, along with copper, which significantly enhances its resistance to sulfuric acid, phosphoric acid, and chloride-induced corrosion.
Applicable ASTM / ASME Standards
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Material Standard: ASTM A182 / ASME SA182 F904L
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Dimensional Standards: ASME B16.5, ASME B16.47
Comparison with Closely Related Grades
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904L vs 316L:
904L offers far superior resistance to pitting, crevice corrosion, and sulfuric acid attack. -
904L vs 254 SMO:
While 254 SMO has higher PREN, 904L is often preferred for reducing acid environments and offers excellent cost-to-performance balance.
Why Stainless Steel 904L Flanges Are Preferred
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Excellent resistance to strong acids
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Very low carbon content minimizes intergranular corrosion
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Non-magnetic austenitic structure
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Long service life with reduced maintenance
Properties & Advantages
3.1 Chemical Composition & Mechanical Properties
Typical Chemical Composition (%)
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Chromium (Cr): 19.0 – 23.0
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Nickel (Ni): 23.0 – 28.0
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Molybdenum (Mo): 4.0 – 5.0
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Copper (Cu): 1.0 – 2.0
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Carbon (C): ≤ 0.02
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Manganese (Mn): ≤ 2.0
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Silicon (Si): ≤ 1.0
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Iron (Fe): Balance
This alloy chemistry provides excellent resistance to both oxidizing and reducing environments.
Mechanical Properties (Typical)
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Yield Strength: ≥ 220 MPa
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Tensile Strength: ≥ 490 MPa
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Elongation: ≥ 35%
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Impact Toughness: Excellent at low and ambient temperatures
904L flanges combine high ductility with reliable strength, making them suitable for pressure piping systems.
3.2 Key Performance Benefits
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Outstanding Corrosion Resistance
Exceptional resistance to sulfuric, phosphoric, and organic acids. -
Superior Chloride Resistance
Strong resistance to pitting and crevice corrosion compared to conventional austenitic grades. -
Excellent Weldability
Fully austenitic structure eliminates risk of solidification cracking when proper procedures are followed. -
Good Formability & Machinability
Suitable for complex flange designs and tight tolerances. -
Long-Term Operational Reliability
Reduced downtime and maintenance costs over the equipment lifecycle.
Types / Variants of Stainless Steel 904L Flanges
We manufacture Stainless Steel 904L flanges in all standard and custom configurations:
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Weld Neck Flanges – High-pressure and high-temperature piping
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Slip-On Flanges – Economical solution for moderate pressure systems
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Socket Weld Flanges – Small bore, high-integrity applications
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Blind Flanges – Line isolation and pressure testing
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Lap Joint Flanges – Systems requiring frequent dismantling
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Threaded Flanges – Non-welded installations
Each flange type is precision-machined to meet international dimensional standards.
Standards & Specifications
5.1 Material & Dimensional Standards
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ASTM / ASME: ASTM A182 F904L, ASME B16.5, ASME B16.47
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EN / DIN: EN 1092-1 (Material 1.4539)
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JIS / Other Standards: Available upon project requirement
5.2 Size & Pressure Range
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Size Range: ½” NB to 48” NB
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Pressure Classes: ASME Class 150, 300, 600, 900, 1500, 2500
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Face Types: Raised Face (RF), Flat Face (FF), Ring Type Joint (RTJ)
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Customization: Non-standard drilling, special finishes, and project-specific tolerances available
Industrial Applications
Oil & Gas
Used in refining units, acid handling systems, and offshore piping exposed to corrosive fluids.
Chemical Processing
Ideal for sulfuric acid, phosphoric acid, and chloride-containing chemical services.
Power Generation
Applied in flue gas desulfurization units, cooling systems, and auxiliary piping.
Marine & Offshore
Resists seawater corrosion and chloride attack in coastal and offshore installations.
Pharmaceutical, Food & Process Industries
Used in process piping where corrosion resistance, cleanliness, and material stability are critical.
Manufacturing Process
As a leading global manufacturer of Stainless Steel 904L Flanges, we follow a controlled and traceable production process:
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Certified Raw Material Selection
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Hot Forging using controlled deformation
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Solution Annealing for optimal corrosion resistance
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CNC Machining to precise dimensions
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Surface Finishing & Final Inspection
Quality Control & Testing
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Chemical composition analysis
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Mechanical testing (tensile, yield, elongation)
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Dimensional inspection per ASME standards
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Non-destructive testing (UT, PT, MT as applicable)
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Hydrostatic testing when specified
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Third-party inspection: BV, TUV, SGS, Lloyd’s
Export Packaging & Documentation
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Seaworthy wooden crates / pallets
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Heat number and traceability marking
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EN 10204 3.1 / 3.2 certificates
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Complete export documentation
Why Choose a Trusted Manufacturer
Choosing the right supplier for Stainless Steel 904L flanges is critical to project success. A proven manufacturer ensures:
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Consistent alloy quality and compliance
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Global standards adherence
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Extensive export and EPC project experience
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Full material traceability
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Long-term partnership and technical support
Connect With Us:
✔ Request a competitive quotation
✔ Download technical datasheets
✔ Consult our engineering and sales experts for project-specific solutions
Frequently Asked Questions (FAQ)
Q1. What makes Stainless Steel 904L flanges different from 316L?
904L offers significantly better resistance to strong acids and chloride-induced corrosion.
Q2. Are Stainless Steel 904L flanges suitable for sulfuric acid service?
Yes, they are specifically designed for sulfuric and phosphoric acid environments.
Q3. Can 904L flanges be welded easily?
Yes. The fully austenitic structure provides excellent weldability with proper procedures.
Q4. What sizes and pressure classes are available?
Sizes from ½” to 48” in ASME Classes 150 to 2500 are available.
Q5. Do you provide third-party inspection and certification?
Yes, inspection by BV, TUV, SGS, or client-nominated agencies is fully supported.
Conclusion
Stainless Steel 904L Flanges represent a proven solution for industries operating in highly corrosive and chemically aggressive environments. Their superior alloy composition, excellent fabrication characteristics, and long-term reliability make them a preferred choice for critical piping systems worldwide.
By partnering with an experienced global manufacturer, buyers gain assured quality, compliance, and dependable supply. Contact our technical sales team today to discuss specifications, pricing, and customized Stainless Steel 904L flange solutions tailored to your project needs.